Wang Zhen, Murigneux Valentine, Le Hir Hervé
Genome Biol. 2014;15(12):551. doi: 10.1186/s13059-014-0551-7.
The exon junction complex (EJC) is a dynamic multi-protein complex deposited onto nuclear spliced mRNAs upstream of exon-exon junctions. The four core proteins, eIF4A3, Magoh, Y14 and MLN51, are stably bound to mRNAs during their lifecycle, serving as a binding platform for other nuclear and cytoplasmic proteins. Recent evidence has shown that the EJC is involved in the splicing regulation of some specific events in both Drosophila and mammalian cells.
Here, we show that knockdown of EJC core proteins causes widespread alternative splicing changes in mammalian cells. These splicing changes are specific to EJC core proteins, as knockdown of eIF4A3, Y14 and MLN51 shows similar splicing changes, and are different from knockdown of other splicing factors. The splicing changes can be rescued by a siRNA-resistant form of eIF4A3, indicating an involvement of EJC core proteins in regulating alternative splicing. Finally, we find that the splicing changes are linked with RNA polymerase II elongation rates.
Taken together, this study reveals that the coupling between EJC proteins and splicing is broader than previously suspected, and that a possible link exists between mRNP assembly and splice site recognition.
外显子连接复合体（EJC）是一种动态的多蛋白复合体，沉积在核内剪接的mRNA上外显子-外显子连接上游。四种核心蛋白，即真核翻译起始因子4A3（eIF4A3）、Magoh、Y14和MLN51，在mRNA的生命周期中与mRNA稳定结合，作为其他核蛋白和胞质蛋白的结合平台。最近的证据表明，EJC参与果蝇和哺乳动物细胞中某些特定事件的剪接调控。
在此，我们表明敲低EJC核心蛋白会导致哺乳动物细胞中广泛的可变剪接变化。这些剪接变化是EJC核心蛋白特有的，因为敲低eIF4A3、Y14和MLN51显示出相似的剪接变化，且与敲低其他剪接因子不同。剪接变化可被eIF4A3的一种对小干扰RNA（siRNA）有抗性的形式挽救，表明EJC核心蛋白参与调控可变剪接。最后，我们发现剪接变化与RNA聚合酶II的延伸速率有关。
综上所述，本研究揭示EJC蛋白与剪接之间的耦合比之前所怀疑的更为广泛，并且在mRNA核糖核蛋白（mRNP）组装与剪接位点识别之间可能存在联系。
